Winterkill in Alfalfa

Mason Keefauver is a Crop Advisor at Centra Sota’s St. Martin location. With spring right around the corner, it is time to start thinking about a successful growing season. Even with a large amount of snow, winterkill in Alfalfa is still something to keep in mind and evaluate as soon as the snow melts.

Mason gave some important insight to what winterkill is, how it’s caused, how its evaluated and what can be done about it. Like most plants’ alfalfa respirates, or exchanges gasses from within the plant to the atmosphere. Unlike a lot of plants, alfalfa goes dormant during the winter and still continues to respirate. Because this plant is still alive throughout the winter, it can incur damage that when spring comes result in the death of the plant.

This damage to the plant occurs when the crown of the plant is subjected to temperatures under 5-15 degrees F. This causes cells in the plant to burst. This is most common when there is little snow fall, because without the snow as an insulator the alfalfa is subjected to extremely cold temperatures. Since snow is porous the plant can still breath or respirate under a blanket of snow. Even with sufficient snow fall alfalfa can still be damaged when snow is blown off of fields. This is more likely to happen when there is not enough residue left in the field or if a cutting is done beyond the recommended September 15th deadline. Another common cause of winterkill is ponding in fields, especially when ice freezes and melts repeatedly. When the ponded water freezes it seals off the air flow to the crown.

Winterkill is most common in older stands. This is because these fields have already incurred damage and are more susceptible winterkill. This damage is a result of regular field activities, like driving over the field and causing compaction. Winterkill is also more likely in plants lacking nutrition. This is because in the winter plants are not able to gain energy through photosynthesis so in the fall the plants collect sugar and this is their energy for the entire winter. This sugar in the plant acts like a kind of “anti-freeze”. Improper pH also makes plants more likely to fall victim to winterkill. The optimum pH for alfalfa is above 6.6, but preferably over 6.8.

Can winterkill be prevented? Mason mentions that although winterkill cannot be prevented, if managed properly the chances it occurs can be drastically reduced. Alfalfa has a cold tolerance rating which dictates how well it should do over the winter. Croplan seed has an especially good guide and scoring system. These scores can be looked at with your Centra Sota Crop Advisor and it can be determined what seed fits your goals and operation best. As mentioned earlier, pH and plant nutrition play huge roles in a healthy plant and preventing winterkill. A 4-5 cut system can put tremendous stress on plants and make them more vulnerable to winterkill. Heavily managed alfalfa fields should be properly fertilized to maintain a healthy and productive crop.

Having plants die because of winterkill can be very costly. This is because this can result in the need for a re-seeding, planting of an emergency crop or for the alfalfa rotation to be cut a year short. If winterkill occurs and nothing is done about it this can cause a decrease is tonnage, feed quality and cause a weed problem.

The best way to evaluate winterkill is to get out into the field as soon as the snow melts. Winterkill can be spotted by looking for brown spots in fields and looking for crowns of plants that show a red-yellow tinge. A brown looking crown may be other damage. The best way to discover winterkill is to dig up plants to look at crowns and roots as well as doing stand counts. Even if fields look green and healthy from the road, they still may have severe damage that can only be seen by taking a closer look. When the alfalfa starts growing, even damaged plants may grow a few green stems, but then die a few weeks later.

In review, winterkill happens in alfalfa as a result or a disruption in respiration during the winter. This can be managed by working with your Centra Sota Crop Advisor to choose an appropriate seed variety and develop a proper fertility plan that will give the plants their best shot at being healthy and productive. To have alfalfa evaluated, as soon as the snow melts let your Centra Sota Crop Advisor know you would like a health check done on your fields.
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